To drill holes in rock, the feeding beam is positioned in parallel with a plane defined by the row of holes to be drilled, especially when loosening rock for further processing. Similarly, in some cases, it is desirable to drill holes in systematic, regular fields in order to be able to perform the blasting as efficiently and accurately as possible. To drill a row of holes in a predetermined direction, the drilling direction is usually determined in x and y planes vertical and perpendicular to each other. Typically, the object is to carry out the drilling in such a way that the y plane is parallel to the longitudinal axis of the carrier, and the x plane is perpendicular to it in order that the drill rod could be positioned more easily in a desired direction. The positioning is typically carried out by means of aligners of different types.
To determine the position of the feeding beam, it is known to use gravity-operated sensing means, whereby the purpose is to detect the direction of the feeding beam with respect to the vertical direction. Such means are described e.g. in SE Patent 392 319, which discloses a sensor box attached to the feeding beam and containing a gravity-operated sensor. This sensor box provides both x-direction and y-direction angle display on a screen positioned in front of the driller. In order to allow for the direction of the boom with respect to the carrier, the sensor box is attached to the feeding beam rotatably about an axis parallel to the drill rod, and the driller can turn the sensor box in proportion to the turning of the boom in such way that the measuring directions of the sensors remain unchanged in relation to the original vertical plane.
GB Patent 1 325 240, in turn, discloses an arrangement in which the feeding beam comprises a control valve, which is operated in response to by a gravity-operated weight sensor and which controls the turning cylinders of the feeding beam during the movement of the boom in such a way that the position of the feeding beam remains substantially unchanged. In this arrangement, the feeding beam and thus the drill rod are first turned to a desired angular position with respect to the end of the boom, whereafter the gravity-operated control valve is positioned vertically and fastened in place. When the displacement of the boom causes the position of the feeding beam to deviate from the original position, the gravity-operated sensor connects one or more of the cylinders turning the feeding beam in operation until the feeding beam has returned to its original direction.
It is also known e.g. from U.S. Pat. No. 4,514,796 and FR Patent 82 00 648 to calculate the direction of the drill rod with respect to the carrier of the drilling equipment by means of various sensors, whereas the direction of the drill rod with respect to the surface of the earth or the force of gravity is not determined in any way, whereby the position of the carrier is not taken into account in any way.
A drawback of the known arrangements is that the alignment is difficult as solely the x and planes can be utilized. The control of the equipment is difficult and the driller has to perform mechanical adjustments and other measures to ensure reasonably successful alignment. The equipments do not reckon with the angle error occurring in cases where the feeding beam is turned both in x and y direction. With known arrangements, angle errors are avoided only when the Turning axes of the feeding beam are turned fully in parallel with the x and y planes, whereby the apparatus has to be displaced for each hole in such a way that the longitudinal direction of the boom is parallel with the y axis or by utilizing a separate additional joint by means of which the feeding beam and its conventional turning joints can be turned in such a way that they are parallel with the x and y planes. The additional joint construction required in the latter case is heavy and expensive, in addition to which additional sensing means are needed to be able to allow for the direction in every case. Moreover, this construction makes the equipment difficult to control and causes extra strains to be exerted both on the boom and the other structures. Furthermore, the known arrangements do not allow for the error caused by the inclination of the carrier when the inclination of the feeding beam is determined by means of sensors responsive to the force of gravity. Finally, the equipments presently in use do not enable accurate determination of drilling depth, but the drilling depth has To be calculated separately while taking into account the inclination of the plane.